Manufacture of aliphatic anhydrides



Patented May 21,1935 9 1 1 2,002,034,

; :1, UNITED STATES PATENT OFFICE MANUFACTURE OF ALIPHAT IG 7 ANnrDRmEs a 1 Henry Dreyfus, LondomEhgland No Drawing. Application October 28, 1932 Serial No. 640,003. In Great Britain December a I 31, 1931 14 Claims. (01. 260 123) This invention relates to the manufacture of conjunction or association with other catalysts aliphatic anhydrides by the thermal decomposicapable of promoting the thermal decomposition tion of aliphatic acids, and especially to the of aliphatic acidSi h ir nhydrid manufacture of acetic anhydride by the thermal Whilst the compounds of the invention may be n decomposition of acetic acid. p oy d in their forms ntaininewater of 5 I have found that compounds containing a crystallizatmn, it s e l l mp y v 1 plurality of metals, one or more of which is at pounds free or substantially free fromiwater of least as electronegative as barium, combined with crystallization Q mDQ iS wh c av been a radicle of a phosphoric acid, are highly useful previously heated to expel water of crystallizacatalysts for promoting the thermal decompositiont -Moreover, y-prc y heating y 0 tion of aliphatic acids into their anhydrides. of the compounds, especially mono or di-meta- The said compounds may contain each of the phosphates, complex poly-metaphosphates can "metals inthe form of basic radicles, i. e. combe produced which are highly suitable forthe pounds which are polymetallic salts of phos purp s the invention.

phoric acids, or one or more of themetals may The thermal decomposition of the aliphatic be present in the form of an acid radicle. Each acids may be performed in anyconvenient way.

of the metals present in the compounds may be For instance, the aliphatic acid vapor may be at least as electronegative as barium, or the passed, in a stream through heated .liquid or compounds may contain more electropositive molten baths consisting of or containing one or metals as well as metals at least as electronegamore of the compounds of the invention. The 20 tive as barium, molten baths may, if desired, contain salts or The following may be mentioned as instances other substances of lowor'relatively low melting of compounds that are very useful for the purpoint which may dissolve or hold in suspension "poses of the invention:potassium barium orthe compounds of they invention; for instancein thophosphate, potassium barium di-, tri-, or cases where the compoundsthemselves are not 25 'tetra-metaephosphates, sodium barium orthomolten at the temperatures employed. As inphosphate, sodium barium di-, tri, or tetrastances of such salts or.substances may be menmeta-phosphates, potassium strontium orthotioned low melting mixtures of sodium chloride phosphate, potassium strontium pyrophosphate, and potassium chloride-or magnesium chloride,-

to potassium strontium dior hexametaphosphates, calcium chloride and magnesium chloride or sodium strontium orthophosphate, sodium stronbarium chloride, or metals or alloys of low melttium pyrophosphate, sodium strontium dior triing, point such as lead or tellurium, alloys there- 'metaphosphates, potassium calcium' orthophosof, or other low melting alloys. l phate, potassium calcium pyrophosphate, potas- Alternatively, the aliphatic acid vapors maybe sium calcium di-metaphosphate, sodium calcium passed in a streamover one or more of the com- 35 orthophosphates, sodium calcium pyrbphospounds'cf the invention contained in tubes or phates, sodium calcium di-, trior hexametaother convenient apparatus and heated to the "phosphates, potassium magnesium orthophosdesired temperature. Thus the compounds may, fphate, potassium magnesium di-metaphosphates, if desired, be employed deposited upon or mixed 4 0 sodium magnesium orthoor pyrophosphates, with carriers or filling materials, and may, if 40 trisodium magnesium triephosphate, sodium desired, be employed in conjunction or in admixmagnesium di trior octa-metaphosphates, ture with other catalysts capable of promoting potassium aluminium orthophosphates, potasthe thermal decomposition of aliphatic acids, into sium aluminium pyrophosphates, purpureo or their anhydridesj 5 1 4s leuteo potassiumvanadium, phosphates, potasf In yet another form of the invention the siumantimony phosphotungstate, calcium aluphatic acids in liquid form and .containingthe minium phosphates, magnesium aluminium compounds of theinvention may be injectedor phosphate, barium aluminium phosphotungstate, sprayed into heated reaction zones; very small calcium phosphotungstates, barium phosphoquantities of the compounds can usefully be emmolybdates, magnesium nickel' orthophosphate, ployed according to this method; For instance, 50

nickel phosphomolybdates, zinc nickel phosphate, acetic acid or other aliphatic acid containing cobalt phosphomolybdates, zinc cobalt phossuch small quantities as about to 2% of one or phate, copper phosphotungstate. more of the compounds, may .be injected or The compounds of the invention may be emsprayed'into theheated reaction zone. 7

ployedas sole catalysts, or may beemployed in The thermal decomposition can be performed 55 Q produced by decompositionof the: corresponding at any temperatures capable of splitting the aliphatic acids into their anhydrides. Usually temperatures between about 300 C. and 900 C. are very suitable, temperatures between about 600 C. and 800 C. being particularly useful.

The aliphatic acids may with advantage be preheated to a temperature approximately equal to or approaching'the reaction temperature prior to subiecting'them'to the thermal decomposition, especially in cases where vapors of the aliphatic acids are to be decomposed. Such preheating may be performed in any convenient manner.

The invention may be applied to the manufacture of aliphatic anhydrides generally. Thus acetic anhydride may readily be -made "from acetic acid, while homologues thereof can be acids, e. g. propionic anhydride can readily be 7 illustrate theinventiombut.arenotto be'understoodas in any way limiting it.

Example;

' .:Acetic .acid :isuvaporized and preheated. to a temperature of 1500C;; itis then passed through a molten bath, comprisingsodium 'chlorideand potassium chloride. in approximately equal proportions and potassium Ibarium tetrametaphos- -:phate.in amount 'equal'to about10%:of themixed chlorides, :and heated to about "700 C. The acetic anhydride formed may' be worked up in any convenient .way.

'- .Example 2 A concentrated solutionEof sodium tungstate and -disodium hydrogen phosphate is rendered neutral by the a'dditionof acetic acid and'broken pumice or other filling -material impregnated therewith; by-treating the massso formed with a warm solution "ofbarium chloridea complex barium phosphotungstate is precipitated on the pumice. The catalytic mass thus prepared, if desired after removal 'of sodium chloride therefrom, for example by washing with water, is heated to about 600 Qandpropionic acid vapor, which has been preheated to about 550 C. is passedover-it; the vapors leaving the reaction zone containa-considerableproportion of propionic anhydrideywhich may be separated .in any convenient way. 7

Example 3 other of which is at least as electropositive as magnesium.

Y vProcess for the manufacture of lower aliphatic anhydrides, which comprises thermally decomposing lower aliphatic acids in the presenceof a catalyst comprising a phosphoric acid in combination Witha plurality of metals at least one of which is atleast as electronegative as barium and another of which is at least as electroposltive as magnesium.

3. Process for the manufacture of acetic anhydride, which comprises thermally decomposing acetic acid in thepresence ofa catalyst comprising a phosphoric acid in combination with a plurality of metals at leastone of which is at .25

leastas electronegative as barium and another of which is at least as electropositive as magnesium.

fl. Process for the manufacture of aceticanhydride, which comprises thermally decomposing acetic acid in the presence of an anhydrous catalystcomprising a phosphoric acid in combination with aplurality of metals at least one of which is at least as electronegative-as barium and another of which .is at leastaselectropositive as magnesium.

5.-Process forthe manufacture of acetic anihydride, which comprises thermally decomposing acetic acid in the presence-of a-catalyst comprising-a phosphoric acid in combination with a plurality-of metals atleast one of which is atleast as electronegative as barium and another of whichis at least as electropositive as-magnesium.

6. Process for the manufacture ofv aceticianhydride, which comprises thermally decomposingacetic acidin the presence of a catalyst comprising a plurality of metals, at least one of which is atleast as-electronegative as barium, and at least one of which is present as an acid radicle, combinedwith a phosphoric. acid. 1 '7. Process for the manufacture of acetic anhydride, which comprises thermally decomposing acetic acid in the presence of a catalyst comprising a polymctaphosphate comprising a plurality of metals at leastone of which is at least as-electronegative as barium.

8. In a process for the manufacture of acetic anhy dride, the step of passing acetic acid through a molten bathcomprising a catalyst which comprises a phosphoric acid in combination with a plurality of metals at leastone of which is at least as electron egative as barium and another of which-is at least as electropositive as magnesium.

9. In a process for the manufacture of acetic anhydride, the step of passing acetic acid ,in contact with acatalyst comprising aphosphoric acid incombinationwith a plurality'of metals at least one of which is at least as electronegative as barium and another ofwhich is at least as electropositive as magnesium and employed in association with an inert carrier. l

10. In aprocess for the manufacture of acetic anhydride, the step of injecting into a'heated reaction zone in a finely divided form aceticacid containing a catalyst which comprises aqphosphoric acid in combination with a plurality of metals at least one of which is at least as electronegative as barium and. another of which is at least as electropositive'as magnesium.

11. Processfor the manufacture of acetic an hydride which comprises passing acetic acid at a temperature between 600 and 800 C. in contact with a catalyst comprising a phosphoric acid in combination with a plurality of metals at least one of which is at least as electronegative as barium. and another of which is at least as electropositive as magnesium.

12. Process for the manufacture of acetican hydride which comprises preheating acetic acid.

and passing it in contact with a catalyst compris-- ing a phosphoric acid in combination with a plurality of metals at least one of which is at least as electronegative as barium and another of which is at least as electropositive as magnesium.

13; Process for the manufacture of acetic anhydride which comprises vaporizing acetic acid,

preheating the vapor, and. passing it at a temperature between 600 and 800 C. in contact with a catalyst comprising a phosphoric acid in combination with a plurality of metals at least one of which is at least as electronegative as barium and another of which is at least as electropositive as magnesium.

14. Process for the manufacture of acetic anhydride which comprises vaporizing acetic acid,

preheating the vapor, passing it at a temperature between 600 and 800 C. in contact with a catalyst comprising phosphoric acid in combination with a plurality of metals at least one of which is at least as electronegative as barium'and another of which is at least as electropositive as magnesium, and separating the acetic anhydride from the water vapor before condensation of the latter.

' HENRY DREYFUS. 

